1. Ease the plant out the pot and remove all the medium.
2. Wash the roots in luke warm water. Gently remove any stuck bits of medium while it's in the water. If any bits are really stuck then leave them.
3. Remove any dead roots (mushy or hollow) with a sharp knife or scissors. Steralise the knife/scissors with a flame if possible and between plants.
3. Wash the roots again with a dash of listerine in the water.
4. Wash the roots again with plain water.
5. Put a layer of new medium in the bottom of the pot.
6. Put the plant in the pot and arrange the roots how I want.
7. Drop more medium in through the gaps in the roots. Keep tapping the pot on the table to work the medium into the gaps. Gently poke bit down into gaps. Fill up the pot bit by bit.
You don't want to pack the medium too tightly. General advise is that you should be able to pick up the pot by holding the leaves of the Phal, but at the same time don't pack too tightly.
Don't worry about air pockets left in the medium. I've had those lots of times and the Phals have still done well (they like air arround the roots anyway).
If you see bugs, you might want to start with the most gentle insecticide like Safer's Soap. If that doesn't work, then you'll have to try the next strongest up the scale. Otherwise you can try Bayer's Advanced Rose and Flower premixed spray. It's systemic and should do the job.